Introduction: The Smoke Detector Head is enclosed in a small cylindrical case 66mm Diameter & 75mm Length. A keyed central locating spigot and four projecting pins enable the head to be plugged into the detector base. The head contains Power Supply, Detector Electronics and an Ion Chamber containing very small quantity of Americium (AM241) radio active material. Material and Components are selected for the Marine Environment. Electronics used supports NFPA 72, ANSI 53.41, and ISO 8201. This circuit is designed to operate in smoke detector systems that comply with UL217 and UL268 specifications.